Adhesive compositions and adhesive sheets



Patented Mar. 1 1 9 UNITED STATES- PATENT OFFICE 2,463,452 I -ADHESIVECOMPOSITIONS AND ADHESIVE SHEETS George W. Yule, Leominster, Mass,assignor to v E. I. du Pont de Nemours & Company, Wilmington, Del., acorporation of Delaware No Drawing. Application August 7 1943,

Serial No. 497,874

'4 Claims. (o 26031.8)

- 2 This invention relates to adhesives and ada masking paper for thesurface protection of hesive sheets, and more particularly, to maskingarticles made from acrylic-type resins. More parpaper having a coatingof adhesive which is norticularly, it is an object to provide a maskingpamally tacky and pressure-sensitive, and to adper having a tacky andpressure-sensitive adhesive compositions for use in the preparation of 5hesive surface of a nature which will permit the such masking papers,stripping of said masking paper from the masked Many uses ofacrylic-type resins require that surface without exhibiting any adhesivetransthe optical properties of these plastics be mainfer, and to provideadhesive compositions which tained to an exceptionally high degree. Ifthe may be applied to a fibrous, backing material to surface of theplastic is scratched or otherwise p o u sue m k p p St r er 0bmarred,its transparency and optical clarity will jects are the provision ermasking paper having begreatly reduced. Therefore, it is necessary to anadhesive coating which is more stable to the protect the surface ofarticles made from these deteriorating eifect of sunlight and aging thanplastics against the abrasive action of dirt, grit, those heretoforeknown, th provision of ad and other substances which will scratch theircompositions which will q e l concentrasurfnce, during shipping,storing, fabricating, astion per unit area of masking surface thansimilar sembly or other handling to which the. articles previously knownad esive co po i o and t e might be subjected. The most practical methodprovision of such adhesives in which a less ex for obtaining positiveprotection of such surpensive extender for the adhesive component mayfaces involves cove ing the same with a masking be employed- Otherobjects will be app m paper. the description of the invention givenherein- A masking paper for use as indicated above a termust possess atacky, pressure-sensitive, adhesive The above j s are c o pl accordingcoating which will permit the mask to be readily to the p e t inventiony pp y g to a fl rOuS applied, and which will hold the mask, afterplacebacking material an adhesive composition comment, tenaciously onthe surface to which it is prising p y o y a ant -adhesive transapplied.However, this adhesive coating must also f r a nt pr f rably an t d al uh this be of such a nature that the masking paper may may be omitted,and an aliphatic, low-boiling, be stripped easily and cleanly from thesurface hydro a bon so v t t e a t evaporating of the plastic withoutleaving portions of the the solvent therefrom so as to produce amaskingadhesive material on the masked surface, 1. e., Paper having a thin,Pressure-Sensitive adhesive the adhesive coating shall exhibit noadhesive coating consisting of the following composition: transfer.Likewise, it is necessary that the adp cent hesive coating be of such acomposition that the Isobutylene polymer 97 to 30 same will notchemically attack or produce sur- Ambadhwive tIanSfeYagent 3 to 10 faceimperfections on the plastic such as crazing, Extender '7 u o to 60frosting, or'swelling. Moreover, these enumerated properties must bemaintained under extreme The polyisobutylene used in the adhesivecomchanEes of temperature, humidity and outdoor expositions of thisinvention serves as the adhesive P 40 agent which supplies the necessarytack or ad- The compositions used, therefore, for such adhesiveness tohold the masking paper to the surhesive coatings have possessed a numberof disface to which it is applied. It is a discovery of advantages.Thus, such compositions have rethis invention that isobutylene polymersposses sulted in masking papers which were deteriorated definitesuperior features over adhesive agents by exposure to sunlight, causingthe loss of the generally employed in pressure-sensitive adnecessaryproperties of a masking paper. Likehesives for two reasons, i. e., theadhesive comwise, previously known compositions have empositionscontaining only polyisobu y n -8 the ployed materials which due to theirsource of adhesive agent in lieu of adhesive agents generally supply,are at times unavailable, e. g., during time used, are extremelyresistant to the deterioration of war. Moreover, such compositions havereeffect of sunlight and secondly, adhesive compoquired the use of arelatively thick coating with sitions containing only polyisobutylene asthe a subsequent use of considerable material peradhesive agent require/2 to M3 less concentration unit area in order to obtain the necessarytack per unit area of paper to acquire the same adand pressuresensitivity. hesiveness as compositions containiiig generally An objectof the present invention is to furnish 5 used adhesive agents.

, which the adhesive is to be applied The anti-adhesive transfer agentsemployed in this invention make possible the removal of the maskingpaper from any surface to which this paper be attached without leavingany adhesive on the surface or fouling the same, i. e., these agentsprevent adhesive transfer. This anti-adhesive transfer agent may be anyplasticizer which is compatible with the polyisobutylene, but is not asolvent therefor, and which is inactive to acrylic-type plastics. Thus,a material which would fulfill all the other requirements for ananti-adhesive transfer agent, but which would be an active plasticizerfor acrylictype plastics would be unsatisfactory in these adhesive'compositions since the use of such a material would result in thecrazing of the surface of the plastic to which it was applied. Thefollowing substances exemplify the type of substances which may beadvantageously used as anti-adhesive transfer agents:

Dibutyl phthalate Dibutyl sebacate Stearic acid Dioctyl phthalate Thepolyisobutylene and the anti-adhesive transfer agent are mixed orcompounded with a solvent in any mixer which may satisfactorily beemployed for the compounding of viscous materials, e. g., churn-mixer,turbo-mixer, or paddlemixer.

The solvent which may be employed in these adhesive compositions mustdissolve not only the polyisobutylene but likewise the anti-adhesivetransfer agent and any extender which may be employed. Moreover, thesolvent in order to be satisfactory for use in the preparation of themasking papers of this invention must not be a solvent for acrylic-typeplastics. Thus, substances such as benzene may not be employed as thesolvent for the preparation of the adhesive compositions according tothis invention since this substance causes crazing of acrylic-typeplastics. Materials which may be satisfactorily employed as solvents,comprise low-boiling, aliphatic hydrocarbons, e. g., 56 Naphthamanufactured by the standard Oil Company of N. J., benzine and the like.The amount of such solvent to be employed depends upon the method by toa paper backing. Thus, since various methods of application require thatsaid compositions possess correspondingly varying viscosities, theoptimum solvent concentration in. the final adhesive must be ascertainedby trial with consideration given to the method of application and theviscosity which will permit the most desirable coating when this methodof application is employed.

These adhesive compositions comprising the polyisobutylene polymer, ananti-adhesive transfer agent, and a solvent, may be spread on apaper-backing material in any practical fashion which will result in arelatively even coating. It has been found that a so-called doctor-knifespreader may be satisfactorily employed to spread the adhesives as auniform and thin coating. After the paper backing has received itscoating, the solvent may be removed by evaporation leaving the finishedmasking paper ready for application to the plastic surface. However, itis not necessary that the masking paper be completely freed of solventbefore application of the mask to plastic surface, thus part of thesolvent may be evaporated from the adhesive coating, the mask applied,and the remainder of the solvent allowed to season out of the coatingthrough the fibrous backing.

Practical circumstances make it usually desirable to employ extenders inthese adhesive compositions- The extender normally will be a materialwhich is less expensive than the polyisobutyie'ne, is of more extensiveavailability, and which does not chemically attack or craze acrylictypeplastics. Any material which is a plasticizer for and compatible withpolyisobutylene, and in which the polyisobutylene is soluble, may beemployed as an extender. provided that this solvent plasticizer does notimpart crazing or any otherwise undesirable characteristics to themethyl methacrylate plastic to which it is to be applied. Aliphatic,high-boiling hydrocarbons have been found advantageous as extenders, e.g., mineral oil.

It has been found that the use of extenders in these adhesivecompositions tends toincrease the tack and likewise the adhesivetransfer tendencies of the adhesive coating. Therefore, when extendersare used in these compositions, more anti-adhesive transfer agent thanis employed in the absence of an extender should be added. A largerquantity of anti-adhesive transfer agent. likewise, is necessary withpolyisobutylenes of lower molecular weight. Accordingly, the optimumcomposition of the adhesive for use as a coating in this inventiondepends upon the molecular weight of the polyisobutylene used and,likewise, upon whether and to what extent an extender is employed.However, it has been found that certain limits to the amount of extenderand the amount of anti-adhesive transfer agent which may be employed,exist. Consequently, when a polyisobutylene having a molecular weightrange between 80,000 and 110,000 is employed, the limit of anti-adhesivetransfer agents is 3% to 10%, Whether or not an extender be employed.Likewise, because extensive use of an extender results in the productionof an unsatisfactory adhesive coating, e. g., a coating possessinginsufficient coherence, the extreme limit of an extender which may beutilized, is between 0% and 60%.

All percentages are expressed throughout as the weight per cent of thecomponent per weight of a total basic adhesive composition, 1. e.,polyisobutylene, anti-adhesive transfer agents, and extenders, exclusiveof the solvent. The quantity of solvent employed is not included in thecalculation of these percentages since the solvent concentration isdependent upon 'the viscosity desired for the particular method ofapplication of the adhesive composition to the fibrous backing material.

Inert fillers possessing a hardness factor less than that of theacrylic-type plastic to which the masking paper is to be applied may beadded to the adhesive coating of this invention, e. g., fine woodsawdust or diatomaceous earth.

The adhesive compositions of this invention may be applied to anypliable sheet material in order to form a desirable masking paper. It ispreferable to employ as a backing material. paper which possesses atleast a moderately adsorbent surface on that side to which the adhesiveis to be applied. Highly calendered papers are not desirable, since thesurfaces of these papers, being relatively nonabsorptive to the adhesivecomposition, -do not permit the maximum adhesion between the adhesivecoating and 'the paper. The reverse surface of the paper-backingmaterial to that receiving the adhesive coating, may be of any naturewhatsoever, and it may be desirable under certain circumstances that thesame possess a waterproof coating. Likewise, papers of the so-calledhigh wet strength type may be employed as backing material. A heavy.unbleached. uncalendered kraft-paper is preferred. Textile fabric orfilms of regenerated cellulose may be employed, but are undesirablebecause of their xpense.

The following examples in which all proportions are by weight unlessotherwise noted. illustrate specific embodiments of this invention:

Example I Parts Polyisobutylene (molecular weight 100,000 100 Dibutylsebacate 10 Mineral oil 100 Benzine 105 The ingredients enumerated aboveare compounded on tumbling rolls and then cut to the desired consistencywith further benzine.

This adhesive composition is then applied as a thin. uniform coating bymeans of a doctor-knife applicator to the surface of 50-pound,unbleached kraft paper. The resulting masking paper is applied to thesurface of cast sheets of polymethyl methacrylate plastic in order toserve as a temporary,protective mask for the plastic sheets. When futureuse of the plastic sheeting requires removal of the masking paper, andafter these plastic sheets have been stored, shipped and handied. thismasking paper may be stripped cleanly from the surface of the plasticsheet. Careful inspection of the surface of the plastic indicates thatno crazing has resulted.

Example II Parts Polyisobutylene (molecular weight 100,000) 100 Stearicacid Mineral oil 100 Low boiling solvent naphtha (completely aliphatic)100 as to serve as a protective coating therefor. After each sheet hasbeen handled, shipped and fabricated into a desirable shape, the maskingpaper may be stripped cleanly and completely from the surface of theplastic. No crazing of the plastic sheeting may be detected.

Example III Parts Polyisobutylene (80,000 molecular weight) Dibutylphthalate 1 Mineral oil 4 Aliphatic low boiling solvent naphtha 30 Theingredients above enumerated are compounded by mixing in a paddle-mixer.The resulting adhesive composition is utilized in the preparation of amasking paper according to the procedure described in Example I. Themasking paper is found to possess a tacky, pressure-senaeeaua 4o Benzinesitive, adhesive coating which permits its easy application topolymethyl methacrylate sheeting. Likewise, this adhesive coating holdsthe masking paper firmly to the sheeting, but also permits the mask tobe stripped cleanly from the surface of the sheeting without leaving anyadhesive thereon.

Exposure of this masked sheeting to sunlight for a period of two weeksresults in no noticeable changes in the properties of the adhesivecoating. Asimilar exposure of the type used previous to this inventionresults in considerable degradation of the desirable properties of thiscoating.

Example IV Parts Polyisobutylene (molecular weight 100,000) 45 Dibutylphthalate 5 Mineral oil 40 Rosin 10 Aliphatic, low boiling naphtha 200The indicated ingredients are compounded by Example V PartsPolyisobutylene (molecular weight 100,000) 50 Dibutyl phthalate 2.5

The above ingredients are compounded into an adhesive composition,applied to 50-p0und unbleached kraft paper, and the solvent evapo-.rated in order to produce a masking paper comprising an adhesive coatingconsisting of 95.25% polyisobutylene and 4.75% dibutyl phthalate. Thismasking paper is readily applied with light pressure to the surface ofpolymethyl methacrylate cast sheeting. Likewise, the mask is readilystripped cleanly and without adhesive transfer from the surface of theplastic. In another case the 2.5 parts of dibutyl phthalate of thisexample are replaced with 1.25 parts of dibutyl phthalate so as toproduce an adhesive coating consisting of 97.56% polyisobutylene and2.44% dibutyl phthalate. In this latter case, the resulting maskingpaper possesses an extremely tacky coating, and when the mask is appliedto the surface of the plastic, it can not be stripped cleanly from theplastic's surface.

It will be understood the above examples are merely illustrative and thepresent invention in its broad phase comprises a removable adhesivesheet comprising a fibrous backing material having a tacky coatingthereon comprising, by weight, 97 %-30% of polyisobutylene and 3%-10% ofan anti-adhesive transfer agent which is a compatible, non-solvent typeplasticizer for polyisobutylene. Preferably, the coating includes also,up to 60% of its weight, an extender which is a compatible, solvent typeplasticizer for polyisobutylene. Where the invention is employed in amasking paper for acrylic-type resins both the anti-adhesive transferagent and extender must be inactive toward acrylic-type plastics.

assaeua The term acrylic-type" resins or plastics is-used herein in itscommon connotation in the artto designate resins or plastics made bythepolymerization of acrylic or methacrylic esters, acids,

of increased hardness or some other desirable property.

An advantage of the present invention is that it provides a removableadhesive sheet which will hold tenaciously to a surface and yet may bestripped therefrom easily and cleanly. A further advantage is that itprovides an improved mask: ing paper particularly adapted for use onacrylictype plastics. A still further advantage is that it provides aneconomical and highly practical removable adhesive sheet stronglyresistant to deterioration under extreme atmospheric conditionsincluding prolonged exposure to sunlight and yet withal avoidscompletely the use of rubber. Moreover, the adhesive of the presentinvention is very economical in that the amount applied per unit area inorder to obtain the requisite tack and pressure-sensitivity isconsiderably less than the amount required of heretofore known adhesivesfor this purpose.

As many apparently widely different embodiments of this invention may bemade without departing from the spirit and scope thereof, it is to beunderstood that the invention is not limited to the specific embodimentsthereof except as defined in the appended claims.

I claim:

1. A removable adhesive sheet comprising a fibrous backing materialhaving a tacky coating thereon essentially consisting of, by -weight, 97%-30% of polyisobutylene having a molecular weight of 80,000 to 110,000,3%-10% of -dibutyl sebacate as an anti-adhesive transfer agent, and upto 60% of mineral oil as an extender.

2. An adhesive for use in preparing removable of dibutyl sebacate asadhesive sheets, said adhesive essentially consisting: of thesubstantially non-volatile components, 9796-3096 of polyisobutylenehaving a molecular weight of .80,000-to 110,000, 3%-10% an anti-adhesivetransfer agent, and up to of mineral oil as an extender, dissolved 'alow-boiling, aliphatic hydrocarbon.

3.-A removable adhesive sheet comprising a flbrous'backingmaterialhaving a tacky coating thereon essentially consisting of, by weight,parts of polyisobutylene having a molecular weight of approximately100,000, 10 parts of dibutyl sebacate, and 100 parts of mineral oil asan extender.

4. An adhesive for use in preparing removable adhesive sheets, saidadhesive essentially consisting of, by weight, 100 parts ofpolyisobutylene having a molecular weight of approximately 100,000, 10parts of dibutyl sebacate, and 100 parts of mineral oil as an extender,dissolved in a low boiling, aliphatic hydrocarbon.

GEORGE W. YULE.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS OTHER REFERENCES I The Resinous Products andChemical 00.,

.Synthetic Resins," article Acryloid-acrysol,"

pages 53 and 56. (Filed in Div. 50 Dec. 5, 1942.)

Strain et al., Ind. and Eng. Chem," Apr. 1939, vol. 31, 382 and 384.

Paper Coatings and Adhesives Based on Vistanex Polybutene, published byAdvance Solvents & Chefrical Corp. (Copy received in Div. 38 Nov. 5,1941.)

Certifieate of Correction Patent No. 2,463,452. March 1, 1949. GEORGE W.YULE It is hereby certified that error appears in the printedspecificatioh of the above numbered patent requiring correction 8.5follows:

Column 8, line 2, claim 2, for the words of the substantially read of,by weight of the substantially;

and that the said Letters Patent should be read with this correctiontherein that the same may conform to the record of the case in thePatent Oflice.

Signed. and sealed this 21st day of June, A. D. 1949.

THOMAS F. MURPHY,

Assistant Uommz'ssz'oner of Patents.

